HERE
7 Maintenance.
7.1 When an ILS is undergoing maintenance, or is radiating for test purposes only, the identification coding will either be removed completely or replaced by a continuous tone.
7.2 Under these conditions no attempt should be made to use the ILS as erroneous indications may be received.
7.3 In the event of an unserviceable Glide Path, the ILS Localiser may be radiating for Localiser only approaches. In which case the identification coding will be radiating. However, it is possible that the Glide Path may also be radiating for setting-up purposes or for flight inspection; it may be subject to interruptions and alterations without warning and may give erroneous indications. In this case ATC will warn all users of this fact and no attempt should be made to use the Glide Path.